IDENTIFICATION OF mRNA ENCODING HOMEOBOX PROTEINS HOX b4 AND HOX b5 IN DEVELOPING CHICKEN GIZZARD TISSUES

Combining reverse transcriptase-polymerase chain reaction (RTPCR) and molecular cloning technologies, we have investigated the expression of homeodomain proteins in chicken gizzard tissues undergoing differentiation. We demonstrate that homeodomain encoding transcripts are found in developing chicken gizzard. An RT-PCR generated 117 bp homeodomain DNA probe was used to screen a gizzard library and resulted in the identification of ~60 potential homeodomain encoding cDNAs. Sequence analysis of the two longest clones identified them as Hox b4 and Hox b5, paralogues of Drosophila Deformed (Dfd) and Sex combs reduced (Scr), respectively. Northern blotting analysis demonstrated an increase in the Hox b4 and Hox b5 mRNAs just prior to the onset of smooth muscle cell differentiation as judged by the expression of the smooth muscle γ-actin gene. Thus, Hox b4 and Hox b5 display the appropriate temporal expression pattern to be involved in the development/differentiation of the chicken gizzard.